Morphologically controlled synthesis of ferric oxide nano/micro particles

ABSTRACT

A thermal method of forming ferric oxide nano/microparticles with predominant morphology is described using different solvents. Methods of using the Fe 3 O 4  nano/microparticles as catalysts in the reduction of nitro compounds with sodium borohydride to the corresponding amines and decomposition of ammonium salts.

STATEMENT OF FUNDING ACKNOWLEDGEMENT

This project was funded by the Deanship of Scientific Research (DSR) atKing Fahd University of Petroleum and Minerals (KFUPM) through ProjectNo. SR161009.

BACKGROUND OF THE INVENTION Field of the Disclosure

The present invention relates to a method of morphologically controlledsynthesis of ferric oxide nano/microparticles.

Description of Related Art

Magnetic nano materials have many potential applications in variousfields due to their well-regulated size and magnetic properties[Abu-Youssef et al. “Synthesis, structural characterization, magneticbehavior, and single crystal EPR spectra of three new one-dimensionalmanganese azido systems with FM, alternating FM-AF, and AF coupling”(1999) Inorg Chem 38:5716-5723]. Iron oxide magnetic nano spheres areeither paramagnetic or super paramagnetic with a size fluctuating from afew nanometers to tens of nanometers. Iron oxide nanoparticles haveattracted considerable attention from for investigators in a wide rangeof disciplines such as magnetic fluids [Caneschi et al. “Cobalt(II)-nitronyl nitroxide chains as molecular magnetic nanowires” (2001)Ang. Chem Int Ed 40:1760-1763], catalysis [Beswick et al. “Iron oxidenanoparticles supported on activated carbon fibers catalyzechemoselective reduction of nitroarenes under mild conditions” (2015)Catal Today 249:45-51], biotechnology/biomedicine [Jain et al. “Ironoxide nanoparticles for sustained delivery of anticancer agents” (2005)Mol Pharm 2:194-205], magnetic resonance imaging [Babes et al. (1999)Synthesis of iron oxide nanoparticles used as MM contrast agents: aparametric study. J Colloid Interf Sci 212:474-482], data storage[Rockenberger et al. “A new nonhydrolytic single-precursor approach tosurfactant-capped nanocrystals of transition metal oxides” (1999) J AmChem Soc 121:11595-11596] and environmental remediation [Baalousha etal. “Aggregation and surface properties of iron oxide nanoparticles:Influence of pH and natural organic matter” (2008) Environ Toxicol Chem27:1875-1882]. Functionalized nanoparticles have found use as chemicalcatalyst [Obermayer et al. “Nanocatalysis in continuous flow: Supportediron oxide nanoparticles for the heterogeneous aerobic oxidation ofbenzyl alcohol” (2013) Green Chem 15:1530-1537], bio-label [Freitas etal. “Iron oxide/gold core/shell nanomagnetic probes and CdS biolabelsfor amplified electrochemical immunosensing of Salmonella typhimurium”(2014) Biosens Bioelectron 51:195-200], and bio-separation [Hola et al.“Tailored functionalization of iron oxide nanoparticles for MRI, drugdelivery, magnetic separation and immobilization of biosubstances”(2015) Biotechnol Adv 33:1162-1176]. They are particularly useful ascatalyst in liquid phase reactions because they are magneticallyseparable from the reaction medium, possess high catalytic activity, andare highly dispersible in solution [Cantillo et al. “Hydrazine-mediatedreduction of nitro and azide functionalities catalyzed by highly activeand reusable magnetic iron oxide nanocrystals” (2013) J Org Chem78:4530-4542; and Moghaddam et al. “Immobilized iron oxide nanoparticlesas stable and reusable catalysts for hydrazine-mediated nitro reductionsin continuous flow” (2014) ChemSusChem 7:3122-3131]. The magnetic momentof the nanoparticles directs the nanoparticles to the target biomoleculeunder physiological conditions.

Nanoparticles have different electrical, optical, magnetic, and chemicalproperties from those of the same material in bulk. It is well-knownthat the properties of nano materials are highly dependent on theirmorphology and structure. In particular, ferric oxide nano materialshaving different morphologies such as nanorods, [Mohapatra et al. “Ironoxide nanorods as high-performance magnetic resonance imaging contrastagents” (2015) Nanoscale 7:9174-9184; and Zhang et al. “Superioradsorption capacity of hierarchical iron oxide@ magnesium silicatemagnetic nanorods for fast removal of organic pollutants from aqueoussolution” (2013) Mater Chem A 1:11691-11697] nanotubes [Wu et al. “Highresponsivity photoconductors based on iron pyrite nanowires usingsulfurization of anodized iron oxide nanotubes. (2014) Nano Lett14:6002-6009] and nanospheres [Disch et al. “Quantitative spatialmagnetization distribution in iron oxide nanocubes and nanospheres bypolarized small-angle neutron scattering” (2012) New J Phys 14:013025;and Khosravi et al. “Adsorption of anionic dyes from aqueous solution byiron oxide nanospheres” (2014) J Ind Eng Chem 20:2561-2567] have gainedconsiderable attention. Ferric oxide has found many applications in manyfields because it is non-toxic, corrosion resistant, chemically stable,and environmentally friendly [Jamil et al. “Synthesis, characterizationand catalytic application of polyhedron zinc oxide microparticles”(2017) Mater Res Exp 4:15902-15910]. Hydrothermal methods [Han et al.“One-step hydrothermal synthesis of 2D hexagonal nanoplates ofα-Fe2O3/graphene composites with enhanced photocatalytic activity”(2014) Adv Funct Mater 24:5719-5727], microwave hydrothermal [Li et al.“Microwave-assisted hydrothermal synthesis of Fe₂O₃-sensitized SrTiO₃and its luminescent photocatalytic deNOx activity with CaAl₂O₄:(Eu, Nd)assistance” (2013) J Am Ceram Soc 96:1258-1262] and microwavesolvothermal [Gutierrez et al. “A Microwave-assisted solvothermalsynthesis of spinel MV₂O₄ (M=Mg, Mn, Fe, and Co)” (2014) Inorg Chem53:8570-8576] are low temperature methods for the preparation ofnanoscale materials of different sizes and shapes. Such methods saveenergy and are environmentally benign because reactions take place inclosed and sealed containers. Synthesis of monodisperse nanometer-sizedmagnetic particles of metal alloys and metal oxides are currently anactive area of investigation because they have potential wide range ofapplications including ultrahigh-density magnetic storage media andbiological imaging. Size, size distribution, shape, and dimensionalitydetermine the properties of the magnetic materials [Indira et al.“Magnetic nanoparticles-A review” (2010) Int J Pharm Sci Nanotechnol”3:1035-1042; and Lu et al. “Magnetic nanoparticles: synthesis,protection, functionalization, and application” (2007) Angew Chem Int Ed46:1222-1244]. Nanoparticles of various iron oxides (Fe₃O₄ and c-Fe₂O₃in particular) have been widely used in wide range of applications. Ironoxide nanoparticles have been used as catalyst for thermal degradationof ammonium perchlorate (AP) and reduction of nitrophenols. Campos etal. [“Chemical and textural characterization of iron oxide nanoparticlesand their effect on the thermal decomposition of ammonium perchlorate”(2015) Prop Expl Pyrotech 40:860-866] studied the thermal degradation ofAP in the presence of Fe₂O₃ catalyst. Xu et al. [“Selective preparationof nanorods and micro-octahedrons of Fe₂O₃ and their catalyticperformances for thermal decomposition of ammonium perchlorate” (2008)Powder Technol 185:176-180] used Fe₂O₃ microoctahedrons and nanorods ascatalyst for thermal degradation of AP. Alizadeh-Gheshlaghi et al.[“Investigation of the catalytic activity of nano-sized CuO, Co₃O₄ andCuCo₂O₄ powders on thermal decomposition of ammonium perchlorate” (2012)Powder Technol 217:330-339] compared the catalytic activities of copperoxide, copper chromite and cobalt oxide nanoparticles. They found thatcopper chromite has the highest catalytic activity in the thermaldecomposition reaction of AP. While the effect of size of thenanoparticle have been examined in details, the effects solvent on sizeand morphology of magnetite (Fe₃O₄) particles and their catalyticproperties is much less understood.

Accordingly, it is the object of the present disclosure to provide asolvothermal method of controlling the morphology of magnetite (Fe₃O₄)micro and nanoparticles at low temperature without the use of anytemplating agent. Also, the disclosure describes the effect ofmorphology and size of particles on their catalytic properties in thethermal decomposition of ammonium perchlorate and the reduction of nitrocompounds by sodium borohydride to the corresponding amines in aqueousmedium.

SUMMARY

A first aspect of the invention is directed to a method of formingferric oxide nano/micro particles comprising:

heating a composition comprising a ferric halide and an alkali metalsalt of a carboxylic acid in a solvent at a temperature of 150-300° C.in a sealed container to form the ferric oxide nano/micro particles,

wherein the ferric oxide nano/micro particles formed by the heating havea predominant morphology, and

wherein the solvent is not ethylene glycol or polyethylene glycol.

In a preferred embodiment, the predominant morphology is selected fromthe group consisting of a porous hollow sphere, a microsphere, a microrectangular plate, and an octahedron.

In another preferred embodiment, the ferric halide is ferric chloride.

In another preferred embodiment, the alkali metal salt of a carboxylicacid is sodium acetate.

In another preferred embodiment, the solvent is at least one selectedfrom the group consisting of water, methanol, ethanol, propanol,isopropanol, butanol, isobutanol, t-butanol, acetonitrile, acetone,dimethylformamide (DMF), tetrahydrofurane, and dimethyl sulfoxide(DMSO).

In another preferred embodiment, the solvent is at least one selectedfrom the group consisting of ethyl acetate, diethyl ether, pentane,isopentane, cyclopentane, n-hexane, cyclohexane, heptane, benzene,toluene, o-xylene, m-xylene, and p-xylene.

In another preferred embodiment, the solvent comprises at least onesolvent selected from the group consisting of methanol, ethanol,propanol, isopropanol, butanol, isobutanol, t-butanol, acetonitrile,acetone, DMF, tetrahydrofurane, and DMSO and at least one other solventselected from the group consisting of ethyl acetate, diethyl ether,pentane, isopentane, cyclopentane, n-hexane, cyclohexane, heptane,benzene, toluene, o-xylene, m-xylene, and p-xylene.

In another preferred embodiment, the solvent comprises at least onefirst solvent selected from the group consisting of ethylene glycol andpolyethylene glycol, and at least one second solvent selected from thegroup consisting of water, methanol, ethanol, propanol, isopropanol,butanol, isobutanol, t-butanol, acetonitrile, acetone, DMF,tetrahydrofurane, DMSO, ethyl acetate, diethyl ether, pentane,isopentane, cyclopentane, n-hexane, cyclohexane, heptane, benzene,toluene, o-xylene, m-xylene, and p-xylene.

In a more preferred embodiment, the solvent is combination of at leasttwo solvents selected from the group consisting of water, ethyleneglycol, polyethylene glycol, and n-hexane.

In another preferred embodiment, the heating temperature is in the rangeof about 195 to 205° C.

In another preferred embodiment, the predominant morphology of theferric oxide nano/microparticle is selected from the group consisting ofporous hollow sphere, microsphere, micro rectangular plate, octahedral,and irregular shape.

In another preferred embodiment, the particle diameter of thenano/microparticles is in the range of about 20 nm to about 25 μm.

A second aspect of the invention is directed to a ferric oxidenano/micro particles having a predominant morphology produced by themethod described herein.

In a preferred embodiment, the predominant morphology of the ferricoxide nano/microparticles is selected from the group consisting ofporous hollow sphere, microsphere, micro rectangular plate, octahedral,and irregular shape.

In another preferred embodiment, the particle diameter of the ferricoxide nano/microparticles is in the range of about 20 nm to about 25.0μm.

A third aspect of the invention is directed to a method of catalyzing areduction of a nitro compound to an amine compound, said methodcomprising:

contacting a solution comprising the nitro compound and sodiumborohydride with a ferric oxide nano/micro particles with predominantmorphology.

In a preferred embodiment, the ferric oxide nano/micro particles have apredominant morphology selected from the group consisting of a hollowsphere, a microsphere, a micro rectangular plate, and an octahedron.

A fourth aspect of the invention is directed to a method of catalyzingthe decomposition of an ammonium salt, said method comprising

contacting the ammonium salt with a ferric oxide nano/micro particleswith predominant morphology.

In a preferred embodiment, the ferric oxide nano/micro particles have apredominant morphology selected from the group consisting of a hollowsphere, a microsphere, a micro rectangular plate, and an octahedron.

In another preferred embodiment of the method, the method furthercomprises heating the mixture to a temperature in the range of 250 to450° C.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows XRD patterns of Fe₃O₄. XRD patterns a-e correspond toproduct A-E, respectively.

FIG. 2 a shows SEM image of Fe₃O₄ product A.

FIG. 2 b shows TEM image of product A.

FIG. 2 c shows hollow spherical aggregates of product A.

FIG. 2 d shows spherical aggregate of product A.

FIG. 2 e shows an HRTEM image of product A.

FIG. 2 f shows an HRTEM image of product A.

FIG. 2 g shows nitrogen adsorption-desorption isotherm and correspondingBJH pore-diameter distribution curve of product A.

FIG. 3 a shows SEM overviews of the microspheres of product B.

FIG. 3 b shows SEM overviews of the microspheres of product B.

FIG. 3 c shows SEM overviews of the microspheres of product B.

FIG. 3 d shows TEM overview of microspheres of product B.

FIG. 3 e shows TEM overview of microspheres of product B.

FIG. 3 f shows TEM of a single microsphere of product B.

FIG. 3 g shows nitrogen adsorption-desorption isotherm and thecorresponding BJH pore-diameter distribution curve (inset) of product B.

FIG. 4 a shows SEM overviews of product C of micro rectangular plateletsof Fe₃O₄.

FIG. 4 b shows SEM overviews of product C of micro rectangular plateletsof Fe₃O₄.

FIG. 4 c shows SEM view of the micro rectangular platelets of Fe₃O₄ ofproduct C.

FIG. 4 d shows the flower-like structure formed by discs of product C.

FIG. 5 a shows SEM overview product D.

FIG. 5 b shows octahedral particles of product D aggregated together inthe form of cylindrical rod.

FIG. 5 c shows several octahedral particles of product D.

FIG. 5 d shows a single octahedral particle of product D.

FIG. 6 a shows the SEM images of product E.

FIG. 6 b shows the SEM images of product E.

FIG. 6 c shows TEM images of product E.

FIG. 6 d shows TEM images of product E.

FIG. 7A shows the diameter distribution histograms of products A.

FIG. 7B shows the diameter distribution histograms of products B.

FIG. 7C shows the diameter distribution histograms of products C.

FIG. 7D shows the diameter distribution histograms of products D.

FIG. 8 a shows TG observations of decomposition of AP in the presence ofFe₃O₄ particles of products A-E.

FIG. 8 b shows temperature dependent plot of loss in mass percentage ofAP in the presence of Fe₃O₄ particles of products A-E.

FIG. 9 a shows a time dependent UV-Visible spectra of reduction of 4-NPcatalyzed by product A in aqueous medium [conditions: [4-NP]=80 μM,[NaBH₄]=8 mM, [Fe₃O₄]=1 μg/L and temperature=22° C.

FIG. 9 b shows plots of ln(A_(t)/A₀) versus time for reduction of 4-NPcatalyzed by product A-E [conditions: [4-NP]=80 μM, [NaBH₄]=8 mM,[Fe₃O₄]=1 μg/L and temperature=22° C.].

FIG. 10 shows a Time dependent UV-Visible spectra of reduction of 4-NPin the absence of catalyst [conditions: [4-NP]=80 μM, [NaBH₄]=8 mM andtemperature=22° C.].

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown. The presentdisclosure will be better understood with reference to the followingdefinitions.

All publications mentioned herein are incorporated herein by referencein full for the purpose of describing and disclosing the methodologies,which are described in the publications, which might be used inconnection with the description herein. The publications discussed aboveand throughout the text are provided solely for their disclosure priorto the filing date of the present application. Nothing herein is to beconstrued as an admission that the inventors are not entitled toantedate such disclosure by virtue of prior disclosure. Also, the use of“or” means “and/or” unless stated otherwise. Similarly, “comprise,”“comprises,” “comprising” “include,” “includes,” and “including” areinterchangeable and not intended to be limiting.

As used herein, the term “compound” is intended to refer to a chemicalentity, whether in a solid, liquid or gaseous phase, and whether in acrude mixture or purified and isolated.

As used herein, the term “salt” refers to derivatives of the disclosedcompounds, monomers or polymers wherein the parent compound is modifiedby making acid or base salts thereof. Exemplary salts include, but arenot limited to, mineral or organic acid salts of basic groups such asamines, and alkali or organic salts of acidic groups such as carboxylicacids. The salts of the present disclosure can be synthesized from theparent compound that contains a basic or acidic moiety by conventionalchemical methods. Generally such salts can be prepared by reacting thefree acid or base forms of these compounds with a stoichiometric amountof the appropriate base or acid in water or in an organic solvent, or ina mixture of the two; generally non-aqueous media like ether, ethylacetate, ethanol, isopropanol, or acetonitrile are preferred.

As used herein, the term “about” refers to an approximate number within20% of a stated value, preferably within 15% of a stated value, morepreferably within 10% of a stated value, and most preferably within 5%of a stated value. For example, if a stated value is about 8.0, thevalue may vary in the range of 8±1.6, ±1.0, ±0.8, ±0.5, ±0.4, ±0.3,±0.2, or ±0.1.

As used herein, the term “alkyl” unless otherwise specified refers toboth branched and straight chain saturated aliphatic primary, secondary,and/or tertiary hydrocarbons of typically C₁ to C₁₀, and specificallyincludes, but is not limited to, methyl, trifluoromethyl, ethyl, propyl,isopropyl, cyclopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl,isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, cyclohexylmethyl,3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl. As usedherein, the term optionally includes substituted alkyl groups. Exemplarymoieties with which the alkyl group can be substituted may be selectedfrom the group including, but not limited to, hydroxyl, alkoxy, aryloxy,or combination thereof.

As used herein, the term “substituted” refers to at least one hydrogenatom that is replaced with a non-hydrogen group, provided that normalvalences are maintained and that the substitution results in a stablecompound. When a substituent is noted as “optionally substituted”, thesubstituents are selected from the exemplary group including, but notlimited to, halo, hydroxyl, alkoxy, oxo, alkanoyl, aryloxy, alkanoyloxy,amino, alkylamino, arylamino, arylalkylamino, disubstituted amines (e.g.in which the two amino substituents are selected from the exemplarygroup including, but not limited to, alkyl, aryl or arylalkyl),alkanylamino, aroylamino, aralkanoylamino, substituted alkanoylamino,substituted arylamino, substituted aralkanoylamino, thiol, alkylation,arylthio, arylalkylthio, alkylthiono, arylthiono, aryalkylthiono,alkylsulfonyl, arylsulfonyl, arylalkylsulfonyl, sulfonamide (e.g.—SO₂NH₂), substituted sulfonamide, nitro, cyano, carboxy, carbamyl (e.g.—CONH₂), substituted carbamyl (e.g. —CONHalkyl, —CONHaryl,—CONHarylalkyl or cases where there are two substituents on one nitrogenfrom alkyl, aryl, or alkylalkyl), alkoxycarbonyl, aryl, substitutedaryl, guanidine, heterocyclyl (e.g. indolyl, imidazoyl, furyl, thienyl,thiazolyl, pyrrolidyl, pyridyl, pyrimidiyl, pyrrolidinyl, piperidinyl,morpholinyl, piperazinyl, homopiperazinyl and the like), substitutedheterocyclyl and mixtures thereof and the like.

As used herein, the term “cycloalkyl” refers to cyclized alkyl groups.Exemplary cycloalkyl groups include, but are not limited to,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, andadamantyl. Branched cycloalkyl groups such as exemplary1-methylcyclopropyl and 2-methylcyclopropyl groups are included in thedefinition of cycloalkyl as used in the present disclosure.

As used herein, the term “aryl” unless otherwise specified refers tofunctional groups or substituents derived from an aromatic ringincluding, but not limited to, phenyl, biphenyl, naphthyl, thienyl, andindolyl. As used herein, the term optionally includes both substitutedand unsubstituted moieties. Exemplary moieties with which the aryl groupcan be substituted may be selected from the group including, but notlimited to, hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy,nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate orphosphonate or mixtures thereof. The substituted moiety may be eitherprotected or unprotected as necessary, and as known to those skilled inthe art.

As used herein, the term “alcohol” unless otherwise specified refers toa chemical compound having an alkyl group bonded to a hydroxyl group.Many alcohols are known in the art including, but not limited to,methanol, ethanol, propanol, isopropanol, butanol, isobutanol andt-butanol, as well as pentanol, hexanol, heptanol and isomers thereof.Since the alkyl group may be substituted with one or more hydroxylgroup, the term “alcohol” includes diols, triol, and sugar alcohols suchas, but not limited to, ethylene glycol, propylene glycol, glycerol, andpolyol.

As used herein, the term “template” refers to as a structure directingagent and is stable under hydrothermal aging conditions and furthermorehydrophobic relative to the metal salts. Many templates used in themanufacturing nanoparticles are known in the art. They include all typesof surfactants including anionic surfactants, cationic surfactants, andneutral surfactants. The surfactant may act as a nucleation site for theformation of the nanoparticles. Alkyl ammonium salts are commonly usedas templates to form structures in solution that interacts with theinorganic material in solution and serve as a template for the growth ofnanoparticles. A commonly used template is tetrapropylammoniumhydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide,or tetrapentylammonium hydroxide. Other known templates include cetyltrimethylammonium bromide, cetyl triethylammonium bromide, or dodecyltriethylammonium bromide. Other known templating agents are polymerssuch as Pluronic F127, Pluronic P123, Brij-56, or Brij-30. The templateis usually decomposed during calcining at temperatures in the range545-600° C. for 6-10 hours.

As used herein the term “predominant morphology” refers to a morphologythat is present in a major amount or an amount that is significantlymore than any other morphology or combination of morphologies in apreparation of nano/microparticles of ferric oxide as observed in SEMand/or TEM images. In the instant disclosure, several predominantmorphologies have been observed by SEM and/or TEM including the poroushollow sphere, microsphere, microrectangular platelet, octahedron, andirregular shape shown in FIGS. 2-6 , respectively.

The present disclosure is further intended to include all isotopes ofatoms occurring in the present compounds. Isotopes include those atomshaving the same atomic number but different mass numbers. By way ofgeneral example, and without limitation, isotopes of oxygen include ¹⁶O,¹⁷O, and ¹⁸O. Isotopes of iron include ⁵⁴Fe, ⁵⁶Fe, ⁵⁷Fe and ⁵⁸Fe.Isotopically labeled compounds of the invention can generally beprepared by conventional techniques known to those skilled in the art orby processes and methods analogous to those described herein, using anappropriate isotopically labeled reagent in place of the non-labeledreagent otherwise employed.

A first aspect of the invention is directed to method of forming ferricoxide nano/micro particles comprising:

heating a composition comprising ferric halide and alkali metal salt ofa carboxylic acid in a solvent at a temperature of 150-300° C. in asealed container to form a ferric oxide nano/micro particles,

wherein the ferric oxide nano/micro particles formed by the heating havea predominant morphology, and wherein the solvent is not ethylene glycolor a mixture of polyethylene glycol and ethylene glycol.

The method is a solvothermal method for preparing ferric oxidenano/microparticle having predominant morphologies using differentsolvents or combinations of solvent. Thermal treatment of a reactionmixture comprising ferric halide and alkali metal salt of a carboxylicacid in different solvents produces different predominant morphologies.The solvent may be a polar solvent, a non-polar solvent or a combinationthereof.

In a preferred embodiment, the solvent is a polar solvent. The polarsolvent can be protic or aprotic polar solvent. Protic solvents include,but not limited to water or mono-, di-, and trihydroxy compound.Monohydroxy compounds include alcohols such as, but not limited to,methanol, ethanol, propanol, isopropanol, butanol, isobutanol,t-butanol, pentanol, cyclopentanol, cyclohexanol, phenol, hexanol,cycloheptanol, heptanol, cyclooctanol, octanol, phenol, or isomersthereof. Dihydroxy compounds include ethylene glycol, propylene glycol,butylene glycol, and oligomer and polymers thereof are particularlypreferred solvents for the method. Also, trihydroxy compounds such asglycerol may be used in the method alone or in combination with anyother solvent. In a more preferred embodiment, the solvent is water,methanol, ethanol, propanol, isopropanol, butanol, isobutanol,t-butanol, ethylene glycol, propylene glycol, butylene glycol, orcombinations thereof.

In another preferred embodiment, the solvent is a polar aprotic solventincluding, but not limited to, acetonitrile, acetone, tetrahydrofuran(THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), orcombinations thereof.

In another preferred embodiment, the solvent is a non-polar solvent suchas a halogenated hydrocarbon including, but not limited tochloromethane, dichloromethane, chloroform, tetrachloromethane,chloroethane, and dichloroethane. Other non-polar solvents include, butare not limited to, diethyl ether, methylethylether, diethylether,pentane, ethyl acetate, isopentane, cyclopentane, n-hexane, cyclohexane,n-heptane, benzene, toluene, o-, m-, or p-xylene, and combinationthereof.

In another preferred embodiment, the solvent is a mixture of polarsolvents and non-polar solvents. The mixture may contains polar solventin the range of 5% to 95%, preferably in the range of 20% to 80%, morepreferably in the range of 30% to 70%, and even more preferably in therange of 40% to 60%, and most preferably in the range of 45% to 55%.

In a more preferred embodiment, the solvent is a mixture of water andethylene glycol or polyethylene glycol, preferably the mixture containswater in the range of 10% to 90%, more preferably. in the range of 30%to 70%, and most preferably in the range of 45% to 55%.

In another preferred embodiment, the solvent is a mixture of non-polarsolvent and ethylene glycol or polyethylene glycol. In a more preferredembodiment, the solvent is a mixture of n-hexane and ethylene glycol orpolyethylene glycol, preferably the mixture contains n-hexane in therange of 10% to 90%, more preferably. in the range of 30% to 70%, andmost preferably in the range of 45% to 55%. In a particular preferredembodiment the mixture contains 50% water in ethylene glycol orpolyethylene glycol.

Any ferric halide may be used in the method including ferric fluoride,ferric chloride, ferric bromide, or ferric iodide. In a preferredembodiment, the ferric halide is ferric chloride.

Similarly, any alkali metal salt of a carboxylic acid may be used in themethod. In a preferred embodiment, the alkali metal salt includes, butnot limited to, one or more of lithium, sodium, or potassium salt. Thesalt may be any carboxylic acid salt such as, but not limited to, formicacid, acetic acid, propionic acid, butyric acid, citric acid, oxalicacid, or tartaric acid. In a particularly preferred embodiment, thealkali metal salt of a carboxylic acid is sodium acetate.

The method may produce nano/microparticle having any morphology. In apreferred embodiment, the morphology of the particle is selected fromthe group consisting of a porous hollow sphere, a microsphere, a microrectangular plate, and an octahedron.

The method includes heating a composition of ferric halide and alkalimetal salt in a solvent at a temperature, preferably substantiallyconstant, for a time in the range of 8 to 36 hours, preferably in therange of 10 to 32 hours, more preferably in the range 12 to 24 hours,and most preferably in the range of 16 to 20 hours. In a particularpreferred embodiment, the time of heating is 18 hours. The heatingtemperature is in the range of 150 to 300° C., preferably in the rangeof 170 to 250° C., more preferably in the range of 190 to 230° C., andmost preferably in the range of about 195 to 205° C. The methoddisclosed herein has several advantages. One advantage of the method isthat there is no need or requirement for a templating agent such astetrapropylammonium hydroxide, tetraethylammonium hydroxide,tetrabutylammonium hydroxide, or tetrapentylammonium hydroxide. Otherknown templates include cetyl trimethylammonium bromide, cetyltriethylammonium bromide, dodecyl triethylammonium bromide, PluronicF127, Pluronic P123, Brij-56, or Brij-30 to obtain the variousmorphologies of Fe₃O₄. Finally, the solvothermal method is carried outat relatively low temperature. Various morphologies of thenano/microparticles of Fe₃O₄ can be obtained by varying the solvent andits composition.

In some embodiment, the ferric oxide nano/microparticle has anygeometrical shape such as, but not limited to, a porous hollow sphere, asphere, a micro rectangular plate, octahedral, or irregular shape.

Similarly, the diameter of the ferric oxide nano/microparticle may varyin the range of 10 nm to about 50 μm depending on the reactionconditions, in particular, the solvent composition. In some embodiments,the particle diameter is in the range of about 10 nm to about 25.0 μm,more preferably in the range of about 20 nm to about 15 μm, and mostpreferably in the range of about 100 nm to about 5 μm.

A second aspect of the invention is directed to ferric oxide nano/microparticles with predominant morphology produced by the method describedherein.

In a preferred embodiment, the morphology of the ferric oxidenano/microparticle is selected from the group consisting of poroushollow sphere, microsphere, micro rectangular plate, octahedral, andirregular shape.

A third aspect of the invention is directed to a method of catalyzing areduction reaction of a nitro compound to the corresponding amine, saidmethod comprising:

contacting a solution comprising the nitro compound and sodiumborohydride with ferric oxide nano/micro particles which have apredominant morphology selected from the group consisting of a hollowsphere, a microsphere, a micro rectangular plate, and an octahedron.

The nitro compound may be any nitro compound such as alkyl or aryl nitrocompound to produce the corresponding amine Many aliphatic and aromaticnitro compounds are known in the art and may be utilized in the methodincluding, but not limited to nitro methane, nitroethane,nitroglycerine, nitrobenzene, dinitrobenzene, trinitrobenzene,nitrotoluene, dinitrotoluene, trinitrotoluene, nitrophenol,dinitrophenol, and trinitrophenol, also known as picric acid.

The method comprises contacting the nitro compound with a reducing agentin the presence of the ferric oxide nano/microparticle with apredominant morphology in a solvent. The reducing agent may be anyreducing agent which is capable of reducing a nitro compound to thecorresponding amine Several reducing agents are well-known in the artincluding, but not limited to hydrogen gas or sodium borohydride. Thesolvent may be any solvent in which the nitro compound is soluble andmay be polar solvent, apolar solvent or mixture thereof. The polarsolvent may be protic solvent such as, but not limited to, water andalcohols such as methanol, ethanol, propanol, isopropanol, butanol,isobutanol, t-butanol, and the like. Also, the polar solvent may bepolar aprotic solvent such as, but not limited to acetone, acetonitrile,dimethylformamide, tetrahydrofurane, dioxane, and the like. In someembodiments of the method, apolar solvent such as hexane, diethyl ether,chloroform, methylene chloride, tetrachlormethane, and the like solventmay be used.

In a preferred embodiment of the method the reaction mixture may beheated to accelerate the reaction, whereas in some other embodiment thereaction may be cooled to dissipate the heat produced by the reaction.

In a particularly, preferred embodiment, the method is carried out inaqueous solution at ambient temperature. The solution may be buffered tomaintain constant pH of the reaction solution. Many buffers are known inthe art depending on the desired pH of the reaction including, but notlimited to, acetate, carbonate buffers, phosphate buffers, Tris, Mops,HEPES, and the like.

A forth aspect of the invention is directed to a method of catalyzingthe decomposition an ammonium salt, said method comprising contactingthe ammonium salt with nano/micro particles described herein. Theammonium salt of the method can be any ammonium salt including that ofammonia, alkyl amines, and aryl amines Any salt of ammonia such as, butnot limited to, ammonium fluoride, ammonium chloride, ammonium bromide,ammonium iodide, ammonium nitrate, ammonium acetate, ammonium oxalateand the like. Other ammonia derivatives such as but not limited tohydrazine and its alkyl and aryl derivatives may be used in the method.Also, the method may utilize ammonium salts of primary, secondary, ortertiary amines as well as aryl amines. Examples of such ammonium saltsinclude but not limited to methylammonium chloride, methyl ammoniumbromide, ethyl ammonium chloride, isopropylammonium chloride, anilinehydrochloride, o-, m-, or p-diaminobenzene hydrochloride, and o-, m-, orp-toluidine hydrochloride. The method comprises mixing the ammonium saltwith nano/microparticles and heating the mixture.

In a preferred embodiment of the method, the nano/microparticles have apredominant morphology selected from the group consisting of a hollowsphere, a microsphere, a micro rectangular plate, and an octahedron.Since the method is carried out with solid material, the method mayinclude step to homogenize the solid material which may includegrinding, mechanical mixing, and/or sonication.

The decomposition reaction may be heated at a temperature in the rangeof 200 to 500° C., preferably in the range of 250 to 450° C. and morepreferably in the range of 300 to 400° C.

The examples below are intended to further illustrate protocols for thepreparation and characteristics of the ferric oxide nano-/microparticlesdescribed above, and are not intended to limit the scope of the claims.

Example 1

Materials and Methods:

Materials:

All the chemicals are purchased commercially and used without anyfurther purification. Ferric chloride (FeCl3.6H2O), sodium borohydride(NaBH4), sodium ethanoate, polyethylene glycol-200, n-hexane, absolutealcohol (e.g., ethanol), ammonium perchlorate (AP), 4-nitrophenol(4-NP), and ethylene glycol (EG) are utilized for the synthesis ofnano/micro particles. Deionized water is used throughout theexperimental work.

Methods:

Catalytic Activities:

(a) Thermal decomposition of ammonium perchlorate-catalyzed by theferric oxide nano/microparticles is studied in a mixture 1% (w/w) ofcatalyst in AP. In a typical experiment, 0.1 g of catalyst and 9.9 g ofAP were mixed and grounded to ensure homogeneity, and the reaction wasmonitored by NEZSCH TGA thermogravimetric analyzer.

(b) The reduction of 4-NP by NaBH₄-catalyzed by the ferric oxidenano/microparticles. In a typical measurement, 1.8 mL of 0.111 mM 4-NPin water, 0.5 mL of 50 mM in water, and 1.0 μg Fe₃O₄ catalyst were addedin a cuvette. Time dependent UV-Vis spectra were recorded between200-500 nm every 5 minutes on UVD3500 spectrophotometer until no furtherchanges at wave length 300 and 400 nm were observed (see FIG. 9 a ).

Structural Characterization:

X-ray powder diffraction (XRD) patterns were obtained on a Rigaku D/maxUltima III X-ray diffractometer with a Cu-Kα radiation source (λ=0.15406nm) operated at 40 kV and 150 mA at a scanning step of 0.02° in range of2θ of 10-80°. Scanning electron microscopy observation was performed ona JEOL JSM-6480A scanning electron microscope. Transmission electronmicroscopy (TEM) observation was performed on an FEI Tecnai G2 S-TwinTEM with an accelerating voltage of 200 kV. Thermogravimetricmeasurements were carried out on NEZSCH STA 409 PC with a heating rateof 10° C./min from 50 to 600° C. UVD3500, Shimadzu was used to monitorthe catalytic reduction of 4-NP.

Example 2

Synthesis of Ferric Oxide Nano/Micro Particles:

A 30 mL solution of 1.35 g of FeCl₃.6H₂O in ethylene glycol is added toa 30 mL solution of 3.6 g of sodium acetate in ethylene glycol andstirred for 30 minutes. The resulting black liquid was transferred toTeflon lined autoclave of 100 mL capacity. The autoclave was sealed at aconstant temperature of 200° C. for 18 h. After heating, the autoclaveis allowed to cool to room temperature, and the product was collected bycentrifugation at 3000 rpm. The resulting product was washed three timeswith deionized water and three times with absolute alcohol. The washedprecipitates were dried in a vacuum oven at 60° C. for 12 h to produceproduct A. The same protocol is used to obtain product B except that theethylene glycol solvent is replaced with 50% aqueous ethylene glycol.Similarly, product C, D, and E are produced by the same method usingpolyethylene glycol, n-hexane, and 50% ethylene glycol in n-hexane,respectively. Table 1 summarizes the solvent composition for productsA-E.

TABLE 1 Comparison of effect of nature and composition of solvent onmorphology and diameter of Fe3O4 particles and their catalyticproperties Catalytic thermal Catalytic decomposition of AP ReductionRed. Of final of 4-NP Solvent Particles Final Temp.^(b) decomp. Temp.K_(app) Composition Morphology Diameter DT^(a) ° C. ° C. ° C. min⁻¹ AEthylene Porous hollow 140 nm 10 285 140 0.4206 glycol sphere B 50%aqueous Microsphere 415 nm 45 329 105 0.3073 ethylene glycol CPolyethylene Microrectangular ~12 μm 90 373 60 0.3054 glycol platelet Dn-Hexane Octahedron ~4.3 μm 20 387 30 0.2834 E 50% n-hexane in Irregular~4 μm 00 360 50 0.2837 ethylene glycol ^(a)Decomposition Temperature.^(b)Temperature of maximum loss in mass percentage.

Example 3

Structural Characterization:

XRD Analysis

XRD patterns of products are shown in FIG. 1 . XRD data analysis showsthat product is Fe₃O₄. The position and relative intensity of alldiffraction lines match well with those of the commercial magnetitepowder (Aldrich catalog No. 31,006-9) reported by Sun et al. [Sun et al.“Size-controlled synthesis of magnetite nanoparticles.” (2002) J Am ChemSoc 124:8204-8205]. The results of XRD data analysis for products A-Dare summarized in Table 2. Diffraction lines analysis of FIGS. 1 a and 1b indicate that product A and B possess monoclinic unit cell structure.In contrast, the results of FIGS. 1 c and 1 d indicate that product Cand D possess face centered cubic unit cell structure. Similarly, Lin etal. and Mckenna et al. have shown that Fe₃O₄ is crystallized in cubicunit cells [Lin et al. “Encapsulated Fe₃O₄/Ag complexed cores in hollowgold nanoshells for enhanced theranostic magnetic resonance imaging andphotothermal therapy. (2014) Small 10:3246-3251; and McKenna et al.“Atomic-scale structure and properties of highly stable antiphaseboundary defects in Fe₃O₄.” (2014) Nat Commun 5:9-10]. Wright et al.[“Charge ordered structure of magnetite Fe₃O₄ below the Verweytransition. (2002) Phys Rev B 66:214422] has determined that Fe₃O₄ iscrystallized in a monoclinic unit cells. The absence of any extraneouspeaks in the XRD patterns indicates that the products are highly pure.The well-defined sharp diffraction lines confirmed that products arehighly crystalline.

SEM and SEM Observation

Table 1 summarizes the morphology and diameter of the products, thesolvent composition used in their synthesis, and their catalyticproperties.

Product A: Porous Hollow Spheres of Fe₃O₄.

SEM and TEM images of product A are shown in FIG. 2 . FIG. 2 a shows anoverview of the product indicating that the particles diameter is smalland formed aggregates. Thus, the morphology of the product and estimateof the average diameter of particles could not be determined by SEM. TEMmicrographs of product A are shown in FIGS. 2 b-d indicating thatproduct A is nearly spherical in shape. The particle diameter is smallabout 10 nm and assembled into large spheres. The large spheres are notuniform in diameter with some irregularity. The spherical aggregates ofnanoparticles appear to be hollow. Also, FIG. 2 c confirms the presenceof hollow spheres with a wide opening at the apical surface indicated byred arrow in the FIG. 2 c . The product Fe₃O₄ is formed by looselypacked nanoparticles leading to small pores (see FIG. 2 d ). The averagediameter of these hollow spheres is approximately 140 nm. Some of thespherical aggregates are visible in microscopic images and probably arefragmented from the large spheres.

HRTEM images of the Fe₃O₄ microspheres and nanospheres obtained areshown in FIGS. 2 e and 2 f It can be seen that the nanoparticleswell-organized and assembled into a single crystal, even though someopen pores and defects are visible in HRTEM images. There are clearboundaries of the assembled small Fe₃O₄ nanoparticles. The particles ofproduct A are hollow which is confirmed by SEM and TEM observations. Theresult presented here shows that the use of ethylene glycol solvent inthe solvothermal method produced a uniform spherical morphology. Thehollow sphere and porous structure may have been resulted from carbondioxide or methane gas trapped inside the spheres. As the temperaturerises in the solvothermal method, the trapped gas pressure in thespheres increases and form a gas bubble leading to increase the diameterof spheres. At certain point, the bubble is burst and the gas escapeleaving an opening and on the pores surfaces. Also, the porosity ofproduct A is examined by nitrogen adsorption desorption isotherm shownin FIG. 2 g . The results indicate that product A is porous withcalculated specific surface area of 35.63 m²/g.

Product B: Microsphere of Fe₃O₄.

Product B is obtained by using 50% ethylene glycol in deionized water assolvent. Product B has been characterized by SEM and TEM and the resultsare shown in FIG. 3 . The SEM observation shows that the product isfairly spherical with no opening. The diameter of these particles variedin the range of 140-415 nm and most particles are about 415 nm. Theproduct appeared as bulk and clustered together due to very large amountof spherical particles present among the product B, see FIGS. 3 a -3 c.

TEM observations, shown in FIG. 3 d-3 f , are in good agreement with theresults obtained by SEM images. Product B is uniformly spherical withdistinct boundaries and compact shape without any irregularities in themorphology. The average diameter of the product measured by TEMmicrograph is approximately 415 nm, and a few nanospheres are alsoobserved along with these nanoparticles.

The edges of these microparticles are very sharp with no zigzagconfirming that the product B is uniformly spherical in shape. The TEMimages show the contrast of light and dark colors that either confinedto the presence of very thin walls/boundaries of the nanoparticles orindicating the presence of cavity inside the spheres. These spheres maybe hollow but no broken microsphere has been observed in SEM and TEMmicrographs. Nitrogen adsorption-desorption isotherm is used foranalysis of porosity of product B, see FIG. 3 g . The isotherm showsthat product B is porous and BET pore diameter distribution iscalculated at 22.9 m²/g.

Product C: Micro Rectangular Platelets of Fe₃O₄.

Product C is obtained by the solvothermal method described herein usingthe solvent polyethylene glycol. It was characterized by SEM and TEM andthe results are shown in FIGS. 4 a-4 d . It is evident from FIGS. 4 aand b that the product is comprised of rectangular disc like particles.The rectangular disc like particles tends to interlink together inlayers and this layer-by-layer assembly leads to different morphologiesas shown in FIGS. 4 c and 4 d . The diameter of these rectangular disclike particles lie in the range of 10 to 20 μm in length and 8-12 μm inwidth. The thickness of these particles is approximately 5 μm (FIG. 4 c). The layer-by-layer assembly of these particles leads to themultilayer thickness and also responsible for the irregular edges. Someof these particles interlink together to form a flower like threedimensional morphology, indicated by red arrow in FIG. 4 d . These discslike particles diffused together at the base and are separated from thefront just like petals of flowers. The addition of further platelets tothe cross leads to the flower shown at the red arrow head in FIG. 4 b .The layer-by-layer arrangement of the platelets develops to theflower-like morphology shown in FIG. 4 d . The edges of the flower shapeFe₃O₄ are very similar to that of original flowers and some of theplatelets oriented upwards acts as stamens (the middle portion oforiginal flowers). There are two possible explanations for the formationof the rectangular platelet of product C. The first is that flower-likestructures are formed, and broken down to the rectangular layer by layerassembled platelets as the temperature rises in the solvothermal method.The other possibility is that the rectangular platelets are formed andarranged in a specific pattern to give rise to flower like structure.The morphology of the majority of product C is the micro rectangularplatelet.

Product D: Octahedron of Fe₃O₄.

The product D was obtained by using n-hexane in the solvothermal method.The morphology of product D was characterized by SEM. The results areshown in FIGS. 5 a-5 d indicating polyhedron morphology. The productconsists of uniform sized octahedra microparticles with eight distinctfaces. Some of particles are not aggregated, see FIG. 5 a . FIG. 5 bshows some others are in aggregated form of the octahedra particleswhich are aligned together in the form of long cylinder.

The size of the octahedra is uniform throughout the product with novariations. The length of the side of the triangle of the octahedron isapproximately 2.5 μm and the average diameter from one end to the otheris about 4.3 μm. Some nanometer sized particles attached on the surfaceof the micro octahedron are observed in SEM micrograph FIG. 5 c . Themicro octahedra appear to be very compact and rigid from the outer andinner surfaces. The edges of the octahedron are uniform and distinctwithout irregularities.

It might be some cubic shaped particles that appeared first further growtowards the edges (each face of polyhedron). The lattice cell appearingat the initiation of the reaction and solvent molecule surrounds it in aspecific pattern that facilitates its growth to an octahedral microparticles. Based on the fact that n-hexane is utilized as solvent insolvothermal synthesis support, an octahedral morphology may beidentified.

Product E: Irregular Morphology of Fe₃O₄.

A mixture of 1:1 (v/v) n-hexane and ethylene glycol was used in thesolvothermal method to obtain product E. The product has beencharacterized by SEM and TEM and the results are shown in FIGS. 6 a-6 d. The SEM results shows some of the particles are irregular shapedembedded in some of the material. At low SEM resolution, it is notpossible to differentiate between different shapes in the product. TheTEM results shown in FIGS. 6 c and 6 d show irregular shaped particlesof few micrometers in diameter. Some of the particles are connected likea net and run to several micrometers in length. In addition to the bigparticles, there are a large number small particles

TABLE 2 Summary of various parameters obtained from XRD pattern analysisof products A-E Parameter Product C and D Product A and B Name ofcompound Magnetite Magnetite JCPDS no. 19-0629 28-0491 Crystal systemCubic Monoclinic Type Face centered Primitive Space group Fd-3m (227)P12/m1 (10) Crystallite size (A) 282 282 Cell parameters a, b and c (Å)8.3851, 8.3851 and 8.3851 5.9444, 5.9247 and 8.3875 α, β and γ(°) 90.0,90.0 and 90.0 90.0, 90.237° and 90.0 Atom coordinates x, y and z of iron0.125, 0.125 and 0.125 0.750, 0.500 and 0.125 0.500, 0.500 and 0.5000.000, 0.500 and 0.000 0.250, 0.250 and 0.250 0.000, 0.000 and 0.5000.500, 0.500 and 0.000 0.500, 0.000 and 0.500 0.750, 0.000 and 0.125 x,y and z of oxygen 0.253, 0.253 and 0.253 0.250, 0.260 and 0.005 0.510,0.500 and 0.755 0.250, 0.240 and 0.495 0.010, 0.000 and 0.255 0.510,0.000 and 0.745 0.010, 0.500 and 0.245 No. of formula units per unitcells (Z)  8.0  4.0 Density (g/cm³)  5.21600  5.2060 Volume (Å³) 591.9225.6 Spacing (d_(hkl)) (Å), 2-theta (°) and 4.84743, 18.286 and (111)5.43, 16.310 and (010) miller indices (hkl) 2.96843, 30.079 and (220)4.05653, 21.892 and (100) 2.53149, 35.429 and (311) 2.88045, 31.021 and(101) 2.42372, 37.061 and (222) 2.715, 32.963 and (020) 2.09900, 43.058and (400) 2.69153, 33.259 and (002) 1.9261, 47.144 and (331) 2.59659,34.513 and (102) 1.71383, 53.416 and (422) 2.20488, 40.895 and (121)1.61581, 56.942 and (333) 1.78442, 51.147 and (212) 1.48422, 62.527 and(440) 1.74586, 52.361 and (201) 1.41918, 65.743 and (531) 1.65292,55.551 and (130) 1.39933, 66.797 and (442) 1.63239, 56.311 and (131)1.32752, 70.934 and (620) 1.39209, 67.190 and (212) 1.28038, 73.969 and(533) 1.3575, 69.141 and (040) 1.26574, 74.970 and (622) 1.34287, 70.004and (132) 1.30996, 72.033 and (123) 1.28733, 73.504 and (140) 1.27756,74.160 and (141) 1.24264, 76.613 and (124) 1.23355, 77.282 and (301)1.21037, 79.047 and (320)

Effect of Solvent Nature and Composition on the Diameter and DiameterDistribution of Products.

FIGS. 7A-7D show the diameter distribution histograms of products A-D.The particle diameter of the products increases in the order: A<B<C<D<E.Non-polar solvent n-hexane was used for synthesis of product E whilepolar solvent ethylene glycol was used for synthesis of product A. Thepolarity of the solvent used during synthesis decreases from product Ato D. It appears that smaller particles sizes are synthesized usingpolar solvents, whereas particles of larger diameters are synthesizedusing non-polar solvents. The diameter distribution of products A-D canbe compared from FIGS. 7A-7D. Diameter distribution histogram of productE is not given because product E possess irregular reef like structures(see FIG. 6 ). All the diameters distribution histograms obeyed Gaussiandistribution and possess one peak only indicating that the diameters ofparticles of products A-D vary in a specific range only. Also, it showsthat particles of products A-D possess homogenous diameter distributionindicating that products A-D are monodisperse. In addition, the fullwidth at half maxima (FWHM) values of the products were calculated andshown in FIGS. 7A-7D. FWHM value of product A and B can be compared witheach because both products contain particles above 100 nm. SimilarlyFWHM value of product C and D can be compared with each other becauseboth products contain particles below 100 μm. The value of FWHM forproduct B is smaller than that of product A indicating that product Bhas narrower diameter distribution than that of product A. This is dueto the lesser polarity of the solvent used to produce product A thanthat of product B. Mixture of two solvents (ethylene glycol and water)was used for synthesis of product B while pure ethylene glycol was usedfor synthesis of product A. Microparticles of product B was synthesizedon oil-water interface, that's why product B possess narrowerdistribution than that of product A. On the other hand, value of FWHMfor product D is smaller than that of product C because polarity ofsolvent used for synthesis of product D is less than that of product C.The graphs of diameter distribution are compared from their respectivevalue of FWHM. It means diameter of particles decreases with increase inpolarity while FWHM value increases with increase in polarity. Ifsmaller size is obtained then size distribution becomes large and ifnarrow size distribution is achieved then diameter of particles becomegreater.

Example 4

Thermal Decomposition of AP Catalyzed by Ferric Oxide Preparations A-E:

FIG. 8 a shows the thermogravimetric results of the decomposition ofAP-catalyzed by the ferric oxide preparations A-E and compared to theuncatalyzed reaction. Thermal decomposition temperature of pure AP is450° C. It is observed that products A-E of ferric oxide have displayedcatalytic activity. The thermal degradation of AP is based on a protontransfer mechanism. The degradation of the AP is initiated by thetransfer of a proton from ammonium ion to perchlorate ion. The thermalenergy provides the required energy to overcome the high energy barrierfor the thermodynamically unfavored proton transfer step. The Fe₃O₄nano/micro particles facilitate the charge transfer step by lowering theenergy barrier. Identical mechanism has been proposed by Chaturvedi etal. [“A review on the use of nanometals as catalysts for the thermaldecomposition of ammonium perchlorate.” (2013) J Saudi Chem Soc17:135-149] and Dey et al. [“Graphene-iron oxide nanocomposite (GINC):an efficient catalyst for ammonium perchlorate (AP) decomposition andburn rate enhancer for AP based composite propellant.” (2015) RSC Adv5:1950-1960] for the thermal degradation of AP in the presence ofmetals.

The porous hollow spheres of catalyst A having almost 140 nm diameterare proved to be the most effective among catalysts A-E. The results inTable 1 and FIG. 8 a show that the final decomposition temperature forthe porous hollow spheres is 310° C. There is almost 140° C. reductionin thermal decomposition temperature of AP when porous hollow are usedas catalyst compared to the uncatalyzed decomposition. The thermaldecomposition curve for this process is very smooth without anyirregularities. Among catalyst A-E, octahedral particles of catalyst Dshowed the lowest catalytic activity. The final decompositiontemperature of AP is 420° C. in the presence of catalyst D. There is adecrease of 30° C. in the final thermal decomposition of AP. Table 1summarizes the results of the thermal decomposition temperatures of APfor catalysts A-E.

FIG. 8 b shows the loss in mass percentage of AP versus temperature forthe uncatalyzed and A-E catalyzed reactions. The extent of decompositionof AP is clearly shown in the figure. The figure shows that thetemperature, at which maximum loss of mass percentage of AP hasoccurred, is different for different catalysts. Interestingly, thedecomposition reaction-catalyzed by the micro rectangular platelets ofcatalyst C shows that all the mass of AP decomposed at once whentemperature reached 373° C. In contrast, all other catalysts show muchbroader decomposition profiles (see FIG. 8 b ). The hollow microspheresof catalysts A and the microspheres B show well defined peaks attemperature 329 and 286° C., respectively. But catalysts D and E show nopeak and continuous decrease in mass of AP over the whole temperaturerange (see FIG. 8 b ). Among all catalysts, catalyst A shows maximumdecrease in thermal decomposition temperature of AP, and catalyst Cshows sharp loss in mass percentage of AP at temperature 373° C.Diameter of particles of catalyst A is the smallest among all catalystsand it shows good catalytic activity. Hence, product A can be consideredas a best catalyst among all the synthesized catalysts.

Example 5

Catalytic Reduction of p-Nitrophenol (4-NP):

Reduction of 4-NP in aqueous media is used as a model to examine thecatalytic activity of Fe₃O₄ micro/nanoparticles in wet media. Fe₃O₄nano/microparticles catalyzed the reduction of 4-NP into 4-aminophenol(4-AP). Time dependent UV-Vis spectra of the reduction of 4-NP by sodiumborohydride-catalyzed by ferric oxide hollow microsphere of product A isshown in FIG. 9 a . FIG. 10 shows the time dependent UV-Vis spectrum ofthe same reaction mixture without the ferric oxide nano/microparticles.Comparison of FIGS. 9 a and 10 clearly show the catalytic activity ofthe ferric oxide nano/microparticles. The observation of two isosbesticpoints in the results shown in FIG. 9 a indicates that the p-nitrophenolis converted to p-aminophenol without accumulation of any reactionintermediate. Since λ_(max) for 4-NP and 4-AP are 400 and 300 nm,respectively, [Farooqi et al. “Effect of acrylic acid feed contents ofmicrogels on catalytic activity of silver nanoparticles fabricatedhybrid microgels.” (2015) Turk J Chem 39:96-107], the reduction of 4-NPis observed by following the UV-Vis spectral change with time. Afirst-order plot of 1n (A_(t)/A_(o)) vs time is non-linear and appearsas a sigmoidal curve. The initial phase is characterized by slowacceleration phase (induction phase) of the reaction followed by rapidreaction phase and a termination phase, see FIG. 9 b . A pseudo firstorder rate constants (k_(app)) were calculated from the straight lineportion of the second phase of the reactions and the results aresummarized in Table 1. The values of k_(app) are in the following order:A>B>C>D>E. This is probably due to the difference in the ferric oxideparticles diameter and morphology. The diameter of ferric oxideparticles decreases in the following order: A<B<C<D<E. It is well-knownthat catalysis is a surface phenomenon. The surface area of particlesdecreases with increasing the diameter. So, it appears that the totalsurface area of the particles increases with decreasing the diameter ofindividual particle. The value of k_(app) for the reduction catalyzedthe porous hollow spheres by catalyst A is greatest among all theproducts. Product A is porous and possesses very small diameter, so itprovides very large surface area for catalysis. The value of k_(app) ofcatalysts D and E is almost the same because their sizes are almost thesame, which confirms dependency of k_(app) on the particles diameter.

The present disclosure describes a method of preparation of Fe₃O₄nano/microparticles with a predominant morphology such as nanosphere,microsphere, spherical aggregates, octahedral, irregular structure,and/or microrectangular plates. The different morphologies observedresult from changing the solvent used in the method preparation. Mostproducts of the method are uniform in shape and diameter distribution,are well separated from each other, and are hollow from the inside withthin and defined boundaries. The nano/microparticles are catalysts forthe decomposition of ammonium perchlorate (AP) and the reduction ofnitro compounds to the corresponding amines. The results show that thecatalysts have good surface properties. Fe₃O₄ catalysts show a trend incatalytic thermal decomposition of AP; with an increase in the diameterof Fe₃O₄ particles, the catalytic properties gradually decrease andparticles with 140 nm diameter decrease the decomposition temperature by140° C. Also, the temperature at which maximum loss in mass percentageof AP occurred was investigated. All the AP decomposed at once at 373°C. when a catalyst with a micro rectangular platelet predominantmorphology was used. Products A-E catalyzed the continuous decompositionof AP over the complete range of temperature. Also, all of the preparednano/microparticles were used as catalysts for reduction of4-nitrophenol. It was observed that the value of k_(app) of thereduction is the largest for hollow microsphere morphology and thesmallest for a catalyst having a rectangular platelet morphology. It wasalso observed that value of k_(app) decreased with increase in diameterof the particles. The above results have shown that these catalysts canbe efficiently used for dry as well as wet processes.

The invention claimed is:
 1. A method of forming ferric oxide nano/microparticles, comprising: heating a composition comprising a ferric halideand an alkali metal salt of a carboxylic acid in a solvent at atemperature of 150-300° C. in a sealed container to form the ferricoxide nano/micro particles, wherein the solvent is hexane, wherein theferric oxide nano/micro particles formed by the heating have apredominant morphology of an octahedron, and wherein the solvent is notethylene glycol or polyethylene glycol.
 2. The method of claim 1,wherein the ferric halide is ferric chloride.
 3. The method of claim 1,wherein the alkali metal salt of a carboxylic acid is sodium acetate. 4.The method of claim 1, wherein the heating temperature is in the rangeof about 195 to 205° C.
 5. The method of claim 1, wherein thecomposition consists of a ferric halide and an alkali metal salt of acarboxylic acid in hexane.
 6. The method of claim 1, wherein a particlediameter of the ferric oxide nano/micro particles is about 4.3 μm. 7.The method of claim 1, wherein the ferric halide is selected from thegroup consisting of ferric fluoride, ferric chloride, ferric bromide,and ferric iodide.
 8. The method of claim 1, wherein the carboxylic acidof the alkali metal salt of a carboxylic acid is selected from the groupconsisting of formic acid, acetic acid, propionic acid, butyric acid,citric acid, oxalic acid, and tartaric acid.
 9. The method of claim 1,wherein the composition is heated for 8 to 36 hours.
 10. The method ofclaim 1, wherein the composition is heated for 12 to 24 hours.
 11. Themethod of claim 1, wherein the composition does not comprise atemplating agent.
 12. The method of claim 1, wherein the ferric oxidenano/micro particles are aggregated.
 13. The method of claim 12, whereinthe aggregated ferric oxide nano/micro particles form a cylinder.